This relates generally to sensors, and more particularly, to touch sensors for electronic devices.
Electronic devices such as portable computers and cellular telephones are often provided with displays. Touch sensitive displays are often used to provide users with the ability to interact with a display through touch-based commands. Touch sensitive displays can be implemented using capacitive touch sensor. Capacitive touch sensors may also be used in forming computer track pads and other input devices.
A capacitive touch sensor may include an array of touch sensor electrodes. In configurations such as those in which the touch sensor is being used as part of a display, the touch sensor electrodes may be formed from pads of transparent conductive material such as indium tin oxide. When a user brings a finger or other external object into the vicinity of the touch sensor electrodes, touch sensor circuitry can detect changes in capacitance on the touch sensor electrodes. These detected capacitance changes can be processed to generate touch event data for controlling an electronic device.
To satisfy consumer demand for small form factor devices, capacitive touch sensor arrays are sometimes formed on thin flexible substrates such as sheets of polyimide. A flexible printed circuit signal bus formed from a separate strip of polyimide can be attached to the edge of touch sensor substrate to route signals from the touch sensor to a logic board within a device.
The signal lines in the flexible printed circuit bus may be attached to the capacitive touch sensor substrate using anisotropic conductive film. Care must be taken not to impose excessive stress on anisotropic conductive film bonds between the flexible printed circuit bus and the touch sensor substrate, because excessive stress may lead to reliability issues. This type of restriction on the amount of acceptable stress for the anisotropic conductive film bonds may impose undesired constraints on use of the flexible printed circuit bus when installing a touch sensor in an electronic device. For example, the acceptable bend radius for the flexible printed circuit bus may be limited. There may also be additional cost and complexity associated with attaching the flexible printed circuit bus to the touch sensor.
It would therefore be desirable to be able to provide improved touch sensors for electronic devices.